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198 STRUCTURE AS ARCHITECTURE▲ 9.17Youth Club, Möglingen, Stuttgart, Germany, Peter Hübner, 1996. Building exterior.architect has created a work of narrative architecture that incorporatestwo seemingly disparate elements – a space-craft and mud. The overallform, and especially the exterior structure, bears strong resemblanceto a space-craft, while the theme of mud is realized by the nonstructuralearthen walls (Figs 9.17 and 9.18). Although the steel ribbeddomeroof and its perimeter open-truss utilize a High-Tech vocabulary,the realistically detailed ‘retractable legs’ speak loudly of space-agetechnology. The source of inspiration behind their detailing, especiallytheir struts and rods that articulate the compression and tension connectionsto the perimeter truss, and the circular landing pads at theirbases, is unmistakable.Wohlen High School is revisited again to discuss the fourth and final setpiecein the school designed by Santiago Calatrava – the library roof. Fromhis preliminary sketches it is clear that the structural form of the roofdraws upon the shape of an open soft-covered book or the out-stretchedwings of a bird flying (Fig. 9.19). 8 It consists of a folded and curved concreteshell whose weight is supported by a tubular steel column reinforcedby ribs whose curved shapes give rise to its spindle-shaped profile.Horizontal stainless-steel rods located around the perimeter of the roof inseveral locations stabilize it by tying it back to structural walls. Daylightwashes down the walls through gaps between them and the roof.▲ 9.18 A primary structural roof supportdisplaying space-age detailing.Although the roof form resembles the pages of an open book or thewings of a bird, the enfolding presence of its curved concrete surfacesimmediately above the mezzanine reading galleries provides a strongsense of enclosure and protection. These emotions, evoked by thecombination of the structural form and the perimeter lighting, reinforce